Toothed belts comprise a body made of elastomeric material having teeth on one of their surfaces, a coating fabric adherent to the surface of the teeth and resistant inserts, hereinafter also referred to as cords, inside the body.
Each component of the belt contributes to increasing the performance thereof in terms of strength, so as to reduce the risk of breaking of the belt and increase the specific power of transmission.
The coating fabric of toothed belts protects the working surface of the belt from wear due to rubbing between the sides of the teeth of the belt and the sides of the slots of the pulley with which the belt interacts and meshes. In addition, the coating fabric prevents the substances present in the environment in which the toothed belt works from possibly damaging it, and reduces the deformability of the teeth and the coefficient of friction on the working surface, i.e., the area of contact between belt and pulley during meshing.
Known is the use of a coating fabric consisting of a single layer, for example, having a weight of between 100 and 500 grams per square meter of surface of fabric, in order to ensure the necessary resistance to abrasion, maintaining an adequate flexibility of the belt when it is winding onto the pulley. Alternatively, also known is the use of a coating made up of a double layer of fabric for improving the characteristics of belt strength and for increasing the operating life of the toothed belt.
The resistant inserts of high performance belts in terms of power of transmission, i.e., for belts that have a specific power of transmission of higher than 25 kW per cm of width, are currently made with steel cords or aramidic-fibre cords, for example, the ones available on the market with the trademarks Kevlar® or Twaron®.
Aramidic fibres, as has been known for some time now, present, however, the disadvantage of having a dimensional stability over time that is very low; consequently, a belt of resistant inserts made of aramidic fibres, during storage, undergoes a shortening of its free development, with consequent alteration (i.e., reduction) of the initial pitch. As a result, during use, the belt is subjected to a higher load and higher stresses, which normally determine an early deterioration, triggered by the meshing error that is generated between the belt and the pulley. Furthermore, resistant inserts made of aramidic fibres require a particularly complex and costly adherization treatment for improving the dimensional stability over time of the resistant insert itself, and moreover, if this treatment is not carried out carefully, it also entails problems during cutting of the belts.
On the other hand, resistant inserts made of steel have a high dimensional stability over time but have a high specific weight and, furthermore, since the depositing of the reinforcement element takes place according to a helical pattern, during cutting of the belts these resistant elements partially come out of the side edges of the belt, with the risk of causing injury to operators during installation of the belt.
In order to prevent the above risk, it is therefore necessary to proceed to a further finishing step, which envisages removal of the strands of cords that protrude as a result of cutting and envisages manual sealing of all the edges of the belt using adhesive in the areas where the filaments partially protrude. This further finishing step involves considerable additional costs, in so far as it has to be carried out manually and has to be performed on each individual belt.
Furthermore, for high powers of transmission, on account of the problems of rapid wear of known rubber belts, there are still used systems of mechanical transmission employing chains or gears, which, however, present disadvantages in terms of weight, noise, maintenance costs and costs due to their complexity owing to the need for lubrication, whilst it would be advantageous to be able to use a rubber belt also for such applications.